1. Field of the Invention
The present invention relates to a state machine for switching between ad-hoc and infrastructure modes to allow concurrent, multiplexed, service of both wireless networking modes.
2. Description of the Related Art
Wireless networking technology has quickly become a widespread method for maintaining network connectivity in both the office and the home. The convenience of being able to maintain connectivity to the network while moving around the office has been the driving force of wireless networking adoption. The first phase of wireless technology adoption was targeted at products that were expected to have connectivity and/or synchronizing capabilities to the network. Personal computers (PCs), laptops, and handheld organizers (i.e., PDAs) are examples of early wireless adoption. However, with competition and proliferation, the cost of wireless technology has dropped tremendously. Now, it is economically feasible to add wireless network capabilities to products that previously have not had such capabilities.
Wireless networking technology uses radio or microwaves to communicate between multiple computers or peripherals connected to the network, whereas wired networks use copper or fiber optic wires. Using wireless technology, a user can transfer files, share an already existing Internet connection, or remotely control or configure another computer or peripheral in the same network without the need for physical wires. Not having to wire an office or a home is an advantage of wireless networking. Another advantage is giving users the ability to use their computers and PDA's while being able to move around a home, office, or public hot spot without having to be plugged into a network. These wireless network devices communicate with the each other via wireless network cards or access points.
FIG. 1 illustrates the basic architecture of a wireless network card containing diversity switch antennae. The three layers of the wireless network card are the physical layer 2, the physical to data link layer 4, and the remaining layers 6. Physical layer 2 has antennae 8, diversity switch 10, band pass filter 12, transmit/receive (T/R) switch 14, power amp 16, RF/IF transceiver 22, loop filter 18, and voltage control oscillator (VCO) 20. Antennae 8 receive and send radio signals. The diversity switch 10 switches between the antennae based on signal strength or based on which antenna was used last for transmission or reception of a radio signal. Band pass filter 12 processes the received signals from antennae 8. T/R switch 14 switches between transmitting and receiving signals. The radio signals are then further processed by power amp 16, RF/IF transceiver 22, loop filter 18, and VCO 20. Physical to data link layer 4 contains baseband processor 24 and media access control (MAC) core 26a. Remaining layers 6 contain host 28.
Using this architecture, wireless network cards currently operate in two modes. The first mode is peer-to-peer or Ad-hoc mode, which allows peer-to-peer networking. In ad-hoc mode, multiple computers or peripherals can network without the need for network credentials, an access point, or other similar wireless networking equipment. FIG. 2 illustrates the state machine for ad-hoc mode. The state machine contains ad-hoc wait state 30 which waits to receive request-to-send (RTS) signals or send clear-to-send (CTS) signals. If an ad-hoc RTS or CTS signal is received or sent, ad-hoc wait state 30 transitions to ad-hoc process state 32, where the ad-hoc process is executed. After the ad-hoc process is executed, ad-hoc process 32 transitions back to ad-hoc wait state 30.
The second mode is LAN or Infrastructure mode. This mode gives a network administrator more control over the wireless network by allowing the wireless channel to be locked down and secure. Infrastructure mode typically requires the user to specify user credentials in order to use the wireless network. FIG. 2 illustrates the state machine for infrastructure mode. The state machine contains infrastructure wait state 34 which waits to receive or send infrastructure RTS or CTS signals. If an infrastructure RTS or CTS signal is received or sent, infrastructure wait state 34 transitions to infrastructure process state 36, where the infrastructure process is executed. After the infrastructure process is executed, infrastructure process 36 transitions back to infrastructure wait state 34.
Both wireless networking modes are viable and useful. However, there are scenarios where having both modes available provides a convenient method for using wireless networking resources. For example, a user can be an unsecured ad-hoc user of a network system while at the same time, the system may require intranet infrastructure to operate the system.
A scenario where both modes of wireless networking may be needed is networked computer projectors. For example, having ad-hoc mode available would allow peer-to-peer networking, which is convenient when a visitor to a company needs to use a projector connected to the company's internal network. The visitor, who has no network credentials, can send presentations to the projector as long has he has his PC wireless card in ad-hoc mode. At the same time, infrastructure mode would allow employees of the company to operate and manage the projector as a networked resource.
Another scenario where dual mode wireless technology may be utilized is in wireless networked printing. For example, in a company, a visitor may need to print documents to a wireless printer. The ideal method of printing would be ad-hoc mode, since it would allow the user to easily send a print job to a printer without network credentials. In the same scenario, infrastructure mode would allow employees of the company, such as a network administrator to securely configure and update the printer as a networked resource.
Yet another scenario where both wireless networking modes are needed is a wireless Internet café. Currently, intranet tracking by the café owner is done using wired methods, while wireless access is offered to the public via ad-hoc mode. Thus, in this setup, existing wireless Internet café's are not completely wireless. The wired side of the network connects to a full service, fixed location PC.
In a 100% wireless Internet café, customer access to the Internet should be via ad-hoc mode for the purposes of allowing easy access to the networking resources. However, the café owner needs to monitor network traffic for charging purposes. Because of security reasons, these activities should be via infrastructure mode. This would enable the café owner to securely track wireless networks from a central wireless computer within the wireless infrastructure.
Currently, most manufacturers of networking products requiring two physical network links will include the capability for either two wired connections or one wired connection and one wireless connection. It may be possible that two wireless connections are supported. In the case of having two wireless connections, one connection would be configured for infrastructure mode and the other for ad-hoc mode.
Some manufacturers have provided two PCMCIA slots for two wireless network cards, with one card operating in ad-hoc mode and the other operating in infrastructure mode. However, as discussed in U.S. Pat. No. 6,665,269, interference and crosstalk from two wireless network cards which are in close proximity from each other present a problem. Since both wireless cards are transmitting at full duplex to the same frequency band, an increase in signal-to-noise ratio results. This is due to the fact that because there are two wireless network cards transmitting at the same time, the physical layer components of each card are essentially noise interferences to the other card. The close physical proximity of the cards' antennae result in the transmissions of the cards colliding with one another. In addition to this, the receiving channels of cards may conflict with each other.
Current wireless cards and antennae were designed to deal with multi-path interference, hence the work to develop the diversity switch antenna model. In this model, when the radio is in receive mode, it will constantly switch between antennae to listen for a valid radio packet. After hearing the beginning sync of a valid packet, the radio will evaluate the sync signal of the packet on that particular antenna, and then switch to and evaluate the other antenna. After evaluating both antennae, the radio will select the best antenna to receive the remaining portion of the packet. While transmitting a packet, the radio will reuse the same antenna that received the packet. If there is a packet failure, the radio will switch to the other antenna.
However, placing two diversity switch antennae within close proximity to each other causes over-correction and unusual interference. In addition, the problem of having two reception antennae is a classic dipole reflection electromagnetic problem. Using two wireless network cards near each other would see noise and interference at each stage of processing, from the antennae to the MAC layer.
To overcome the previously stated problem, it would be preferable to provide concurrent service between the two wireless networking modes using a single, modified, wireless network card. It would be preferable to use a state machine to switch between the two wireless networking modes. It would also be preferable to have a dual MAC core in the single wireless card that can concurrently support both wireless networking modes.